The present invention relates to an electric setting drive for an automotive vehicle speed control or regulating system having an electric motor, a gearing connected to the motor, an electromagnetic rapid-disconnect coupling, and elements for transforming a rotation of the gearing into a linear motion which can be transmitted via a pull cable to a spring-loaded throttle valve.
Such known setting drives are used for an automotive vehicle speed regulation in which the automotive vehicle maintains a preselected speed by automatic displacement of a throttle valve, or for an automotive vehicle speed control in which control of the speed of the automotive vehicle takes place as a function of the position of the gas pedal.
A known electric setting drive has a DC motor employed as an electromotive drive which converts signals produced by an electronic controller into a mechanical movement, a clock duty ratio of the signals being modulated. In order to actuate a throttle valve or gas rod, the electric motor is connected to a driven member of a setting member via a gearing and an electromagnetic rapid-disconnect coupling. The driven drive of the setting member consists essentially of a driven gear which converts a rotation into a linear movement which can be transmitted via a pull cable to the gas rod for the displacement of a throttle valve. The throttle valve is at all times acted on by a spring which, for reasons of safety, urges the throttle valve into the idling position. The opening of the throttle valve by the setting drive must therefore take place in opposition to external resetting forces which can influence the position of the setting drive. For this reason, in the known setting drives, a relatively expensive feedback is necessary which produces a position report signal which corresponds to the position of the setting drive and is compared in a position regulator with an output signal of a speed regulator or of a speed control and, via a motor drive stage, controls the motor of the setting drive until the latter assumes the position orderd by the speed regulator or the speed control. The rapid-disconnect coupling serves the purpose of maintaining a force lock between a motor of the setting drive and the gas rod in the normal control or regulating operation, and of rapidly disconnecting the motor if the vehicle brake or clutch is actuated with a corresponding signal being given off by the brake-light or clutch switch. The throttle valve is then moved back into the idle position by the spring which acts on it. In the known electric setting drive, a coupling element of the electromagnet rapid-disconnect coupling is a pinion of a gearing which can be swung transverse of its longitudinal axis by means of a hinged armature and an electromagnet. If, while the vehicle is under way, the throttle valve is to be actuated by the speed regulator or speed control, the hinged armature of the electromagnet swings the pinion into engagement while a spur gear of the gearing. In order to disconnect this rapid-disconnect coupling upon interruption of the current through the electromagnet, the pinion is pulled out of engagement with the spur gear by a return spring. This electric setting drive therefore also presents the disadvantage of wear of the spur gear and/or the pinion which wear necessarily takes place as a result of the coupling processes.